Arsenic (As) mobility in water is worldwide studied since its toxicity was proven in 1888. Intake of As can lead to skin disease, cancer, kidney and heart failure, diabetes and paralysis. In the Netherlands, groundwater used for drinking water production contains As in the range from 0 – 70 μg/L. Currently, all groundwater treatment plants reduce As in drinking water below the WHO standard of 10 μg/L. However, to ensure no adverse health effects occur by the intake of drinking water, Dutch drinking water companies investigate implications of distributing water with As concentrations below 1 μg/L. The new target value causes 58% of the treatment plants with measurable As in the raw water (19% of all total groundwater treatment plants) to need some sort of adjustment to their treatment scheme to comply with the new As target value...